Lol, well channeled Nana.
Gussets give a better fit at the legs, and I find because the elastic tends to be thinner than on un-gusseted PUL covers, you feel okay about doing them up nice and tight, because they don't leave marks. You wouldn't get a marks problem with your fleece covers I don't think, but I love gussets for PUL covers. Nana said who do gussets, I think Imse Vimse *might* do gussets too? And Bambineo?
Tots Bots sizing is large, BUT the PUL is very thin and so material in the middle is just puffy, not bulky at all.

It might be worth trying a gusseted cover Maz, it's best described by actually seeing one in action. I'll have a hunt around and see if I have any to lend that I can spare, but I can't think of any that aren't in high demand here. I'll have a looksee though.